The present invention relates to an optical switch, and in particular to a distributed optical switch.
Many industries utilise optical switches in their equipment. For instance, the telecommunications industry utilises optical switches in optical dedicated protection and optical shared protection rings (OSPR""s). Optical transmission systems are often constructed with a fault recovery mechanism so that if there is a complete loss of transmission capability due to component and/or transmission line failure, the traffic can be reallocated to other physically diverse routes. Pending U.S. application Ser. No. 09/349,349 (incorporated herein by reference) describes such an OSPR system.
Switches are commonly incorporated in OSPR""s at network nodes. At a network node, a 2xc3x972 switch may be utilised to connect between working and protect transmitters/receivers and working and protect transmission lines. Although the OSPR is designed with a fault recovery mechanism, performance of the node will be seriously affected if a switch fails, or has to be removed for maintenance or in order to be replaced. In such an instance, switch failure maintenance can interrupt both working and protection traffic.
FIG. 1 shows a working (2) and protect (4) transmission line connected to respective working and protect receivers (6,8) via a 2xc3x972 switch (10). Similarly, the working and protect transmission lines (2xe2x80x2,4xe2x80x2) may be connected to the working and protect transmitters (6xe2x80x2,8xe2x80x2) via a 2xc3x972 switch (10xe2x80x2). Alternatively, a bidirectional 2xc3x972 switch and a combination transmitter/receiver can be used before the outgoing and incoming paths are routed to transmitter and receiver respectively. This allows these two switches to be combined into one (not shown).
A 2xc3x972 switch allows independent connection of working and protection optical channels (or transmission lines) to working or protection receiver or transmitter as appropriate. This functionality is required in both 1+1 (in which the same data is simultaneously transmitted along both the working and protection lines, providing redundancy in the event of either of the lines failing) and 1:1 protection switching (in which high priority data is typically transmitted along the working line, low priority data along the protect line; in the event of the working line failing, the high priority data is routed along the protect line).
FIG. 2 shows how such bidirectional 2xc3x972 switches may be incorporated into an OSPR module 20, which includes an optical cross connect (oxc) 22. The OXC contains optical switches to route traffic off and on the shared protection as described in U.S. application Ser. No. 09/349,349. An OSPR will be comprised of nodes.
The above description is merely an example of how such an optical switch can be used. Many systems, not limited to telecommunications may utilise such optical switching arrangements. The failure of a switch, or a part of the switch, inevitably affects connectivity between the inputs and outputs, as does removal of the switch for repair or maintenance. The present invention aims to address some of the problems of the prior art.
In a first aspect, the present invention provides an optical switching segment comprising at least one input, at least one output, at least one connector arranged to be connectable to a further segment so as to provide at least one of a further input and a further output, and a switch arranged to selectively connect between two of said input, said output and said connector. Thus, such a segment could be installed in a network as part of an optical switch that is distributed; thus failure of any one segment, or its removal, need not affect all of the connectivity of the switch.
Preferably, said connector provides a further input and said switch is arranged to selectively connect said output to one of said input or said connector.
Alternatively, said connector provides a further output and said switch is arranged to selectively connect said input to one of said output and said connector.
In another aspect, the present invention provides an optical switch comprising at least two segments, each segment having a respective input and a respective output, arranged such that in use if a first segment is removed, a second segment can operate as a pass-through device.
In a further aspect, the present invention provides an optical switch distributed over at least two cards, the first card having a first input and a first output, and the second card having at least one of a second input and a second output, the switch further comprising a switching means arranged to selectively form a connection between two of said first input, said first output, and said second input and output, arranged such that said second card may be removed from communication with said first card whilst the switch is in use, said first card then being arranged to connect said first input to said first output.
Preferably, said cards are removably attached. Alternatively, detachment of the cards may require destruction or damage to one or more of any components that connect the cards, e.g. the cutting of an optical fibre connection.
Preferably, connecting means between the cards comprises at least one of a freespace optical beam path and a waveguide.
Preferably, said switching means comprises a selection from the group of polymer waveguides, mach-zehnders and MEMS (micro-electro mechanical systems).
Preferably, said switching means utilises the control of a selection from the group of reflection, refraction and diffraction to perform the switching.
The switch may further comprise a port for providing control signals to said switch.
In another aspect, the present invention provides a telecommunications system comprising a switch as claimed in claim 4.
Preferably, said switch is connected to a system, the respective inputs and outputs being selectively coupled together as required by an operator.
Preferably, a first portion of the switch is arranged to act as a pass-through device if a second portion of the switch is removed from the system.